A recently developed method that couples a I-D duct flow solver to a 3-D general purpose Computational Fluid Dynamics (CFD) solver is described. This methodology provides an integrated approach for the solution of coupled flow and heat transfer problem, utilizing ID and 3D meshes for fluid flow. During the solution process, principles of conservation are preserved at the interface of the two flow domains. Results from the coupled ID/3D simulation are then verified by comparison to the 3D solution, and are validated against an empirically obtained correlation for a shell and tube heat exchanger.